Approximately 60 patients will be enrolled with highly suspected lung cancer, or head and neck cancer. The patients must also be starting radiotherapy or a chemoradiotherapy regimen (except with 5-fluorouracil). The patients will undergo 3 visits. One screening, one pre therapy PET/CT imaging visit, and one (3-5 weeks after the start of therapy) post PET/CT imaging visit. This study will evaluate the FLT and FDG images for tumor proliferation rates for early assessment of tumor response to radiation or chemo-radiation combo.